European Space Agency set for historic comet landing attempt

Ukraine's Klim Churyumov, astronomer and co-discoverer of comet 67P/Churyumov-Gerasimenko, talks to media at the European Space Agency ESA in Darmstadt, Germany, Wednesday, Nov.12, 2014. Europe's Rosetta space probe was launched in 2004 with the aim of studying the comet and learning more about the origins of the universe. On Wednesday, Nov. 12, 2014 the Philae lander detached from Rosetta and started it's descent to the 4-kilometer-wide (2.5-mile-wide) 67P/Churyumov-Gerasimenko comet. (AP Photo/Michael Probst)
(The Associated Press)

The image released by the European Space Agency ESA on Wednesday, Nov. 12, 2014 shows Rosetta controllers in the control center in Darmstadt, Germany, celebrating after the Philae lander has separated from ESA's Rosetta orbiter and started its descent to the surface of comet 67P/Churyumov-Gerasimenko. European Space Agency said Wednesday that the landing craft separated from Rosetta probe for descent to comet 67P. (AP Photo/ESA, Juergen Mai) MANDATORY CREDIT
(The Associated Press)

Celebrating scientists in the main control room appear on a video screen at the European Space Agency after the first unmanned spacecraft Philae landed on a comet called 67P/Churyumov-Gerasimenko, in Darmstadt, Germany, Wednesday, Nov. 12, 2014. Europe's Rosetta space probe was launched in 2004 with the aim of studying the comet and learning more about the origins of the universe. (AP Photo/Michael Probst)
(The Associated Press)

BERLIN – A historic attempt to land a spacecraft on a comet is poised to be set in motion Wednesday by scientists at the European Space Agency, despite a last-minute problem with the landing system.

It would be the climax of a decade-long mission to study a 4 kilometer (2.5 mile) wide lump of dust and ice known as 67P/Churyumov-Gerasimenko. It will also be the end of the decade-long, 6.4 billion-kilometer (4 billion-mile) journey that Rosetta and its sidekick lander Philae traveled together to reach the comet.

ESA announced late Tuesday that the active descent system, which uses thrust to prevent the craft from bouncing off the surface, could not be activated. Instead, the agency is relying on ice screws and a harpoon system to secure the lander.

"The cold gas thruster on top of the lander does not appear to be working so we will have to rely fully on the harpoons at touchdown," said Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.

"We'll need some luck not to land on a boulder or a steep slope."

If all goes to plan, the washing machine-sized lander will separate from Rosetta at 0835 GMT (3:35 a.m.) and drift down to the comet, where it will latch on using harpoons and screws. During the descent scientists will be powerless to do anything but watch, because the vast distance to Earth — 500 million kilometers (311 million miles) — makes it impossible to send instructions in real time.

Confirmation of a landing, if successful, should reach Earth by about 1603 GMT (11:03 a.m. EST).

The plan is that Rosetta and Philae will then accompany the comet as it hurtles toward the sun and becomes increasingly active as it heats up. Using 21 different instruments they will collect data that scientists hope will help explain the origins of comets and other celestial bodies.

The European Space Agency says that even if the landing doesn't succeed, the 1.3 billion euro ($1.62 billion) mission launched in 2004 won't be a failure. Rosetta will be able to perform 80 percent of the mission on its own.